1. Field of the Invention
The present invention relates to a method and device for coating or mixing granular products, in particular food products, more in particular nuts, more in particular peanuts, with a substance.
2. Description of Related Art
Coating devices are known, for instance for coating seeds.
Nuts are traditionally coated in a rotary drum having a horizontal rotation axis. The drum is quite large, i.e. has a diameter of about 1.5-3 meter and a distance between the end walls of about 1 meter.
A batch of nuts is supplied into the drum. A coating substance which is often provided to coat nuts, is generally a combination of powder (or coating mix) and a water based liquid. The powder generally comprises starches and salt, sugar and can contain seasoning and/or flavourings and/or colouring ingredients. The water based liquid is generally sprayed into the drum separately. Other ingredients may also be added. Some of the ingredients may be dissolved in the water based liquid prior to mixing with the nuts. The nuts, coating mix and liquid are mixed inside the compartment during the rotation of the bottom part.
After being coated with the coating substance, the nuts are fried in oil for a short period of time or oven roasted (or air/dry roasted) for some period of time. The result is a nut covered with a coating layer.
In the present invention, it was recognized that a coater having a horizontal axis of rotation is quite cumbersome. The coating process takes quite long. Moreover, the coating process is quite dependent on human operators and it was found to be very difficult or impossible to automate this coating process.
Furthermore, the size of the known coating drum for nuts is quite large and the known drum requires a lot of space. This is a further disadvantage.
Other devices for coating other kinds of products are also known. For instance, some coating devices may have a vertical axis of rotation. Generally the bottom part is rotary and a vertical circumferential side wall is stationary.
In the present invention, the insight was developed that known vertical axis coaters are quite problematic for various kinds of granular products, in particular nuts and more in particular peanuts. It was recognized that the coating substance is quite sticky, and tends to stick to every part of the coater i.e. the bottom and the side walls.
DE 19750042 A1 discloses a method and device for coating a granulate with a coating layer. U.S. Pat. No. 5,582,643 discloses a centrifugal tumbling granulating-coating apparatus for coating high quantities of a powder or granular material in batches. DE 4411058 A1 discloses a rotary spray coating unit for seed or other granular materials.
The coating substance also tends to stick to utensils inside the coater, such as an atomizer disk, baffles for mixing the mass, the exit opening and other parts. This stickiness not only makes the operation cumbersome, but also hinders cleaning of the device and the utensils. Cleaning however is essential for maintaining the required processing and hygienic circumstances.
Therefore, coaters having a vertical axis of rotation were found to be unsuitable for various granular products, in particular sticky products such as coated nuts, more in particular peanuts.